Equilibrium and kinetic controls contribute to nitrogen and oxygen isotope effects during anammox in a wastewater treatment system
- 1Aquatic and Isotope Biogeochemistry, Department of Environmental Sciences, University of Basel, Basel, Switzerland
- 2Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Air Pollution / Environmental Technology, Dübendorf, Switzerland (paul.magyar@empa.ch)
- 3Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Process Engineering, Dübendorf, Switzerland
- 44Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Surface Waters - Research and Management, Kastanienbaum, Switzerland
Anammox plays a pivotal role in both natural and engineered systems as a process that simultaneously converts fixed nitrogen to N2 and regenerates NO3–. In aquatic and terrestrial ecosystems, isotopic measurements, especially of the NO3– pool, provide an essential constraint on the processes that regulate the supply and elimination of fixed nitrogen, but the isotope effects of anammox remain poorly constrained.
We present measurements of the δ15N and δ18O of NO3–, NO2–, and NH4+ as processed by anammox in a mixed microbial community enriched for N removal from wastewater. We find that oxygen isotope effects expressed in NO2– include a substantial contribution from equilibration reactions with water superimposed on kinetic isotope effects. Equilibrium between water and NO2– during processing by anammoxis greatly accelerated above rates observed under abiotic conditions even during growth phases when NO2– is rapidly being consumed. In turn, δ18O of NO3– nearly completely reflects the incorporation of O atoms derived from water with little additional isotopic fractionation. The δ15N values of NO3– and NO2– also show evidence for an equilibrium isotope exchange reaction between these molecules, which raises the possibility that nitrite oxidation is partially reversible, while introducing a high degree of variability into the δ15N of NO3– generated by anammox. Finally, variation observed in the δ15N of NH4+ consumed by anammox can be connected to physiological limitations within the anammox cell.
Despite this complexity, we were able to use NO2– and NO3– isotope measurements to diagnose changes in the activity of anammox and related processes within the wastewater treatment system during a low-temperature perturbation experiment. These results provide new constraints for interpreting the variability in δ15N and δ18O of NO3–in natural systems, with implications for estimating relative rates of fixed N turnover processes.
How to cite: Magyar, P., Hausherr, D., Niederdorfer, R., Huang, K., Mohn, J., Bürgmann, H., Joss, A., and Lehmann, M.: Equilibrium and kinetic controls contribute to nitrogen and oxygen isotope effects during anammox in a wastewater treatment system, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4677, https://doi.org/10.5194/egusphere-egu23-4677, 2023.
